In this project we determined the major antigenic relationships of various rotavirus strains derived from humans and animals. Elucidation of the neutralization specificities of rotavirus is important in order to achieve a more comprehensive understanding of rotavirus epidemiology and for formulation of an effective strategy for vaccination. For example: (i) the bovine rotavirus strain NCDV-Cody which was originally isolated from a diarrheic calf and traditionally considered as the virulent counterpart for the attenuated NCDV-Lincoln (VP7 serotype 6) was shown to carry VP7 serotype 8 and VP4 serotype 6; (ii) the human rotavirus strain 69M (VP7 serotype 8) which was originally isolated from a child with diarrhea in Indonesia, was found to possess a new VP4 neutralization specificity which was closely related antigenically to equine rotavirus H-2 VP4; (iii) the human rotavirus strain MT19 which was originally isolated from a diarrheic child in Brazil was found to have a strong two-way cross-neutralization relationship with porcine rotavirus serotype 5 (OSU strain) and serotype 11 (YM strain); (iv) the vervet monkey rotavirus strain SA11 was shown to possess a distinct VP4 neutralization specificity which was related in a one-way fashion to rhesus monkey rotavirus MMU18006 VP4.